Polyphenylene sulfide has been utilized in the electronic field because it has good flow properties due to its crystallinity and good heat resistance and water resistance. However, when polyphenylene sulfide is used as molding materials, it has a defect of poor toughness (impact strength), so it is difficult to utilize it for various moldings, particularly large moldings.
In order to eliminate the above defect, a number of attempts for blending or alloying polyphenylene sulfide with various resins, various thermoplastic elastomers or the like have been proposed.
For example, JP-B-56-34032 describes resin compositions excellent in moldability and flammability consisting of polyphenylene oxides and polyphenylene sulfides. JP-A-58-27740 by the present applicant describes a modified block copolymer composition excellent in impact and delamination resistance consisting of polyphenylene sulfide or other engineering resins and a hydrogenated block copolymer modified with α,β-unsaturated carboxylic acid derivatives. In JP-A-58-40350, the present applicant also proposes a thermoplastic graft copolymer excellent in impact resistance consisting of polyphenylene sulfide or other engineering plastics, a hydrogenated block copolymer modified with α,β-unsaturated carboxylic acid derivatives and epoxy group-containing polymers. JP-A-58-154757 describes a polyarylene sulfide resin composition excellent in impact resistance and moldability/processability consisting of polyarylene sulfide and a copolymer of α-olefin/α,β-unsaturated acid glycidyl ester. JP-A-59-207921 describes a resin composition excellent in impact resistance consisting of polyphenylene sulfide, polyolefin graft-copolymerized with an unsaturated carboxylic acid or its anhydride or their derivatives and an epoxy resin. JP-A-62-153343, JP-A-62-153344 and JP-A-62-153345 describe polyphenylene sulfide resin compositions excellent in impact resistance consisting of a specific polyphenylene sulfide and a copolymer of α-olefin/α,β-unsaturated acid glycidyl ester. JP-A-62-169854, JP-A-62-172056 and JP-A-62-172057 also describe polyphenylene sulfide resin compositions excellent in impact resistance consisting of a specific polyphenylene sulfide and polyolefin graft-copolymerized with an unsaturated carboxylic acid or its anhydride or their derivatives.
On the other hand, regarding resin compositions comprising polyphenylene sulfide and polyphenylene ether, the use of copolymers having specific functional groups as additives are proposed for the purpose of improving their compatibility. For example, JP-A-01-26616 and JP-A-02-75656 describe methods of using copolymers of styrene and ethylenically unsaturated monomers having an oxazolyl group for improving the compatibility of acid-modified polyphenylene ether and modified polyphenylene sulfide. JP-A-01-213359, JP-A-01-213361, JP-A-02-86652 and JP-A-05-339500 describe methods of using copolymers of styrene and ethylenically unsaturated monomers having a glycidyl group for improving the compatibility of polyphenylene ether and polyphenylene sulfide. JP-A-03-20356 describes a method of using copolymers of styrene and ethylenically unsaturated monomers having an oxazolyl group for improving the compatibility of polyphenylene sulfide and polyphenylene ether.
However, the materials design of the resin compositions disclosed in these prior art references is not adequate in terms of dispersibility of resin compositions consisting of polyphenylene sulfide and polyphenylene ether, and in toughness and weld strength of the resulting moldings.
Moreover, JP-A-09-161737 discloses that compositions using copolymers of styrene and ethylenically unsaturated monomers having an oxazolyl group for improving the compatibility of polyphenylene sulfide and polyphenylene ether can be utilized as a case for a sealed alkaline secondary battery. However, under the present situation, even the compositions disclosed therein are inadequate in terms of dispersibility of a dispersed phase, and in toughness and weld strength of the resultant moldings.
Incidentally, resin material applications have been currently expanding into applications for power sources for driving mobile equipment, power sources for computer data backup, solar batteries for the purpose of effective utilization of solar energy, and various secondary batteries in terms of environmental protection. It is well known that secondary batteries are frequently used for supplying required electric power to the internal combustion engines of automobiles. Moreover, the so-called electric vehicles which directly utilize secondary batteries as driving power sources in place of internal combustion engines are under energetic development. Thus, demand for secondary batteries tends to grow increasingly as industrial technologies develop, and requirements for further decrease in size and weight together with increase in electric capacity are increasing.
Battery cases (containers) for holding an electrolytic solution and electrodes, sheets for battery cases and films for battery cases are essential to secondary batteries. The main properties required for the resin materials for battery cases first include resistance to electrolytic solutions. For example, various resistances are required, such as, resistance to aqueous alkaline solution for alkaline storage batteries; resistance to organic electrolytic solution (for example, an organic electrolytic solution comprising a solute of lithium hexafluorophosphate (LiPF6) and a solvent of propylene carbonate/1,2-dimethoxy ethane) for lithium ion batteries; resistance to oils for use in automobile applications; and resistance to acids for lead storage batteries.
In addition, secondary batteries are required to appropriately maintain the properties of electrolytic solutions for a long period of time. For example, for an alkaline storage battery, the battery performance may be deteriorated when water in an aqueous alkaline solution in a battery case is permeated to the outside of the battery cell. On the other hand, for a lithium ion battery, the battery performance may be deteriorated due to the decomposition of a lithium salt (for example, lithium hexafluorophosphate (LiPF6) or lithium tetrafluoroborate) in an organic solution when water enters into a battery case from the outside. Further, the performance capable of enduring heat generation and increase of internal pressure associated with chemical change during charging and discharging is also required.
Furthermore, sealed secondary batteries are especially required to be compact and lightweight wherever possible, and to have large electric capacity with long battery life. Therefore, cases for sealed secondary batteries should have good toughness (impact strength, elongation) when they have thin wall thicknesses. Moreover, they are required to be excellent in heat resistance, thermal creep resistance, and thermal rigidity so that they can endure harsh conditions such as heat generation and increase in internal pressure during charging and discharging. And these requirements are the same also in the field of sheets for battery cases.
Polypropylene resins and ABS resins have been mainly adopted for these resin materials for secondary battery cases. However, polypropylene resins are excellent in flowability during molding, resistance to hot water permeability (resistance to water vapor permeability), and resistance to gas permeability, but they have defects such as large molding shrinkage percentage, poor rigidity, particularly poor rigidity at high temperatures and poor thermal creep resistance, in the injection molding of products having structures with thin wall thicknesses and ribs. On the other hand, ABS resins are inadequate in durability to gasoline and oils (for example, brake oil and preservatives) and have high hot water permeability and high gas permeability when applied to automobile applications, so they cannot maintain the properties of an electrolyte when used for a long time and cannot satisfy essential requirements of secondary batteries that the electric capacity shall be ensured over a long time. On the other hand, the polyphenylene sulfide resin compositions disclosed in the prior art references described above satisfy the above performance requirements for materials for secondary battery cases (containers, sheets and films), but they have problems in terms of dispersibility of a dispersed phase, and in toughness and the weld strength of moldings, as described above.